This invention relates to a perforated, closed cell foam padding material useful with orthopedic devices.
Treatment of body skeletal abnormalities such as bone fractures usually involves the immobilization of a portion of the body, which is normally provided by some form of casting material. For a long time casting material was made of plaster of paris or fabric impregnated with plaster of paris; these materials have many disadvantages, among them being unduly heavy, not sufficiently strong in many instances, and not being impervious to water and other fluids. More recently, casts have been made of materials such as Fiberglas and polyurethane for the reasons of lighter weight, greater strength, and imperviousness to liquids so as to allow the patient to immerse the affected limb in water for bathing, swimming or for physical therapy. Although these improved casting materials lived up to their original promise, very little attention has been given to the padding material under the cast, which is a prime component of the casting system. Such casts normally must remain in place on the body for a long period of time and often result in considerable discomfort and trauma to the patient. Traditionally cotton fabric, polypropylene and other materials of this nature have been used as padding material under casts to provide protection for the skin under the cast. However, such materials absorb moisture and thus accumulate moisture and cause the padding to become soggy; thus, the standard technique of using an electric hair dryer for drying the padding, through the layers of the casting material, was a long and arduous procedure. Unless the padding material is kept reasonably dry, itching, skin irritation and development of fungal infection may result, the problem being accentuated by normal perspiration. Moreover, soggy padding material does not serve its intended function of decreasing the discomfort and trauma to the patient cuased by chafing and pressure against the cast by various protuberances of the anatomy.
A variety of other materials have been tried, with minimal success, to provide a cast padding material which will not absorb moisture, that will allow for moisture vapor transmission and which will provide a resilient cushion between the cast and the body. Such materials include stockinet material of knitted or woven, non-wetting, crystalline polypropylene material (U.S. Pat. No. 3,881,473), sleeves made of non-wetting polyethylene or polypropylene yarn (U.S. Pat. No. 3,882,857), and a closed cell polymeric foam formed of polyethylene, polypropylene, polyurethane or polystyrene (U.S. Pat. No. 4,294,240).
Considering the disclosure of U.S. Pat. No. 4,294,240 in greater detail, the four specifically named foam materials are relatively non-wettable because of theclose packing of their molecular structure. Only some of them are sufficiently soft and pliable to serve as a padding between the underlying bony prominences and the rough undersurface of the cast. However, these materials do not allow for rapid transit of water molecules toward and into the perforations in the padding surface. The clinical application of the preferred perforated polyethylene foam material resulted in a high percentage of untoward skin reactions because the padding simply wouldn't dry even with extended application of heat to the outside of the cast; it retained a film of water between the skin and the padding material. The reason such perforated closed cell polyethylene foam does not perform acceptably is believed to be due to the electro-chemical attraction between the material surface and water molecules which, in terms of contact angle (i.e., the electro-chemical angle betwen the axis of a water molecule and the surface of the material) is quite high. Because of the high contact angle, the time required for transit of moisture entrapped under the closed areas of the foam to the perforations, where it can evaporate through the cast material, is so long as not to allow complete removal of moisture from under the padding material when heat is applied to the cast. Apart from its relatively high contact angle, the surface of polyethylene foam is relatively rough with the consequence that water molecules are trapped in the hills and valleys of the surface thereof confronting the skin. Although the surface can be made smoother by increasing the density of the closed cell foam, it is at the expense of reduced elasticity and brittleness to an extent that it no longer will acceptably conform to the surface of the encased extremity.